LM9040M datasheet(8/10 Pages) NSC

8 / 10 page

Open Input Pins Defaults (Continued)

In the cases where both the inverting and non-inverting pins

are open the non-inverting condition (ie

voltage divider

across the output) will be the dominant condition

Any common mode signal seen by inverting input pin should

not be allowed to exceed the Common Mode voltage range

Exceeding the positive Common Mode voltage limit could

cause the inverting input pin voltage comparator to act as if

the inverting input pin is open Since the comparator circuit

is not part of the switched capacitor network there is no

frequency limitation on the signal to the comparator Any

transient on the inverting input pin which goes above the

comparator threshold will immediately cause the output to

switch to the open sensor mode The output will return to

normal operation when the voltage on the inverting input

falls below the comparator threshold

Supply Bypassing

For best performance the LM9040 requires a VCC supply

which is stable and noise free The same 5V VREF supply

used for the AD converter is the recommended VCC sup-

ply During operation the device will generate current spikes

coincident with the clock edges Inadequate bypassing will

cause excessive clock noise on the outputs as well as

noise on the VCC line The LM9040 VCC pin should be by-

passed with a minimum 01 mF capacitor to the Signal

Ground pin and should be located as close to the device as

possible

Some applications may require an additional

47 mF tantalum capacitor especially if there are several

other switched capacitor devices running off the same 5V

supply line The Signal and Digital Ground pins should be

tied together as close to the device as possible

TLH12372 – 21

FIGURE 11 Typical Application

LM9040M Datenblatt(PDF) 8 Page - National Semiconductor (TI)